Number 84 (Story #1), June 15, 1992 by Phillip F. Schewe and Ben Stein GALLEX OBSERVES SOLAR NEUTRINOS at a rate of 83 Solar Neutrino Units (SNU). The multi-nation collaboration (U.S. contact: Richard Hahn at Brookhaven, 516-282-4337) detects solar neutrinos in a 50,000 liter bath of gallium chloride installed in the Gran Sasso tunnel under the Abruzzi Mountains in Italy. The neutrinos, arising largely from proton-proton fusion reactions in the Sun, but also from the decay of beryllium and boron in the Sun, convert a gallium-71 nucleus into a germanium-71 nucleus. The radioactive Ge is extracted every three weeks and monitored closely in a separate vessel. The calculated production rate of 83 SNU (1 SNU = 10**-36 neutrino captures per atom per second) is to be compared with theoretical estimates that range from 124 to 132 SNU. For the 132-SNU estimate, 74 SNU should come from (relatively low energy) pp reactions, 34 SNU from Be-7 decays, 14 SNU from B-8 decays, and 10 SNU from N-13 and O-15. The Gallex results are much closer to the theoretical estimates than those from the South Dakota or Kamiokande (Japan) detectors, which are sensitive only to the higher energy B and Be neutrinos; these two earlier detectors typically observed only one third the neutrinos prescribed by the Standard Model of solar physics. The Gallex results are in stark contrast with those from SAGE, a fourth detector group, located in the Former Soviet Union. SAGE last year reported finding essentially no neutrinos from pp reactions. (Paper give last week at the Neutrino 1992 meeting in Grenada, Spain. Also P. Anselmann et al., upcoming article in Physics Letters B.)